Drying of carrot slices using infrared radiation

Carrot slices were dried from initial moisture content of 8.52 kg water kg⁻¹ dry matter to 0.11 kg water kg⁻¹ dry matter by infrared dryer. Experiments were conducted using three levels of infrared power (300, 400 and 500 W) and at air velocities (1.0, 1.5 and 2.0 m s⁻¹). The effects of process variables on the drying kinetics of carrot, drying time, specific energy consumption and quality parameters of dried carrot (shrinkage, rehydration ratio and colour) were investigated. The drying time at infrared power of 300, 400 and 500 W was 252 and 277 min, 205 and 236 min, and 145 and 155 min at air velocities of 1.0 and 2.0 m s⁻¹, respectively. The drying rate increased with increasing infrared power. The specific energy consumption values varied between 12.22 and 14.58 MJ kg⁻¹-evaporated water for all the drying conditions. Shrinkage, rehydration ratio and colour parameters were found to be affected by process variables.     

Single Layer Drying Characteristics of Half Fruit Tomato

Drying kinetics of half fruit tomatoes were investigated in a laboratory dryer at the temperature of 35–65°C and air velocity of 0.13–1.00 m/s. The optimum drying conditions in terms of drying rate, colour and growth of microorganisms were also identified. Drying rate and shrinkage increased significantly with the increase in air temperature. But the red colour (a?) decreased significantly with the increase in air temperature. Drying rate increased with the increase of air velocity up to 0.75 m/s. The optimum drying air conditions was the temperature 55°C and air velocity 0.75 m/s, when drying time, colour, ripeness and growth of microorganisms were considered. Microorganisms (molds and fungus) were grown at or below 40°C temperature and it could be prevented by sodium metabisulphite pretreatment. The experimental data were fitted to six different single layer drying models and Midilli-Kucuk-Yapar model was found the best to predict the moisture content.     

超声处理对中短波红外干燥红枣时间及品质的影响

为提高红枣干燥品质,减少干燥时间,以干燥时间为响应值,响应面优化得到红枣中短波红外干燥前超声处理条件为：频率40 kHz、时间40 min、功率350 W。最优超声处理后中短波红外干燥红枣至其干基含水率约为40%时所需干燥时间为9.55 h;未超声处理中短波红外干燥需13.33 h;传统热风干燥需17.13 h。扫描电镜观察红枣果皮,超声处理40 min使果皮表面产生大量裂缝,表皮层变薄,仅38.8 μm,表皮层和亚表皮层易分离,利于干燥过程中水分扩散,显著缩短中短波红外干燥时间。红枣超声处理后中短波红外干燥的干制品品质显著优于未超声处理红外干燥,极显著优于传统热风干燥。最优超声处理条件结合中短波红外干燥,所得干制品在3 种处理方式中总VC、总酚、总黄酮含量最高,糖酸比最高,色泽最优,能耗最少,是适合红枣干燥的技术方法。     

High-humidity hot air impingement blanching (HHAIB) enhances drying behavior of red pepper via altering cellular structure,pectin profile and water state

In order to exploring a feasible pretreatment technology of red pepper, an emerging thermal pretreatment technology namely high-humidity hot air impingement blanching (HHAIB) was employed and its effect on drying behavior and related mechanisms were explored through analyzing the ultrastructure, the contents and composition of cell wall pectins, water state of red pepper during the blanching process under blanching temperature of 110 °C and relative humidity of 35%–40% for various exposure times ranging from 0 to 150 s. Results indicated HHAIB can extensively reduce the drying time from 11 h for the un-blanched samples to 8 h for the samples blanched for 90 s. In addition, HHAIB reduced the products' hardness by 8.19%–47.91% compared to the untreated samples. The cellular structure and water state experienced a significant alternation with the increasing blanching time. The content of water-soluble pectin (WSP) increased, while the contents of chelate-soluble pectin (CSP) and sodium‑carbonate-soluble pectin (NSP) decreased during the blanching process. Overall, HHAIB treatment is a promising blanching technology for red pepper as it can accelerate the drying process through softening tissue and altering the ultrastructure and moisture binding state.Industrial practiceDrying is one of the most frequently used methods for red pepper preservation as it can effectively reduce the moisture content so as to hinder the growth and reproduction of microorganisms and the moisture-mediated deteriorative reactions. While the existence of waxy hydrophobic layer covered the surface of red pepper results in long drying time and poor products' quality. In industrial practice chemical dipping is often used to remove the wax layer and enhance the drying rate of red pepper. However, the chemical residues can trigger food safety issues and how to deal with the highly corrosive chemical dipping solution is also a challenge. Therefore, it is very tempting for industry to explore innovative pretreatment for red pepper drying. The current work indicated that HHAIB is a promising alternative technology to replace the chemical dipping method as it extensively enhances the drying process of red pepper.     

Degradation kinetics of total phenolic compounds,capsaicinoids and antioxidant activity in red pepper during hot air and infrared drying process

Degradation kinetics of total phenolic compounds, capsaicinoids and antioxidant activity in red pepper during both hot air drying and infrared drying were investigated, as well as the correlation between antioxidant compounds and antioxidant capacity was discussed in current study. The fractional conversion kinetic and first order kinetic models were proved to describe the changes of total phenolic compounds vs. drying time and moisture content, respectively. Degradation of capsaicinoids and antioxidant capacity vs. drying time and moisture content both followed fractional conversion kinetic model. Infrared drying accelerated the degradation rate of total phenolic compounds and capsaicinoids vs. drying time as compared with hot air drying at the same temperature; however, a contrary result was found that infrared drying decreased the degradation rate of both total phenolic compounds and capsaicinoids vs. moisture content. Total phenolic compounds exhibited a stronger relationship with antioxidant capacity of red pepper analysed by multiple linear regression analysis.     

Infrared drying of button mushroom slices

The effect of different infrared power levels on the drying kinetics of button mushrooms was investigated. Mushroom slices were dried at infrared power levels of 83, 125, 167, and 209 W. The power level affected the drying and rehydration characteristics of mushroom slices. Drying time was reduced from 300 min to 40 min as the infrared power level increased from 83 to 209W. Mathematical models frequently used to represent drying of agricultural products were fitted to experimental data of mushroom drying. The parabolic model was the best for representation of mushroom drying. Effective moisture diffusivity varied from 3.81×10^?10 to 4.20×10^?9 m²/s over the infrared power levels used. The activation energy was estimated using a modified Arrhenius-type equation and calculated to be 7.55 kW/kg.     

MATHEMATICAL MODELLING OF THIN-LAYER DRYING OF KIWIFRUIT SLICES

The effect of temperature on the drying kinetics of kiwifruit was investigated. The drying process was carried out at temperatures of 50, 55 and 60C, air velocity of 2.4   m/s and relative humidity between 10–25%. Drying time decreased considerably with increased air temperature. Drying process took place in the falling rate period. Twelve mathematical models available in the literature were fitted to the experimental data. The models were compared by four statistical parameters; i.e., determination of coefficient, mean relative percent error, reduced chi-square and root mean square error, and the best-fit model was selected. The modified Henderson and Pabis and Verma et al. models were given the best results in describing thin-layer drying of kiwifruits. The effective diffusivity of water during air-drying varied from 1.743 to 2.241  ×  10 ^{− 10}   m²/s over the temperature range investigated, with activation energy equal to 22.48   kJ/mol.

PRACTICAL APPLICATIONS

Drying can be described as an industrial preservation method in which water content and activity of agricultural products are decreased by heated air to minimize biochemical, chemical and microbiological deterioration. Kiwifruit has a very short life because of softening and vitamin loss during cold storage. The use of drying prolongs the shelf-life of the kiwifruit, as the water content reduction slows down deterioration reactions. In this study, drying characteristics of kiwifruits were studied in a convectional hot-air dryer. The objectives of the present study were to determine experimentally the thin-layer drying characteristics and rehydration capacity of samples, and to fit the experimental data to 12 mathematical models available from the literature.     

The effects of middle infrared radiation intensity on the quality of dried tomato products

The effects of air temperature (T) (unheated and 35 °C), infrared radiation intensity (IP) (894, 1004, 1190, 1314 and 1410 Wm^?2) and air velocity (Av) (1.0, 1.5 and 2.0 ms^?1) on drying characteristics of tomatoes, drying time (DT), specific energy consumption (SEC) and quality parameters were investigated. DT and SEC varied between 114 and 249 min, 10.04 and 18.22 MJ kg^?1 water, respectively, and were significantly affected by process variables. Shrinkage ratio (S) and rehydration ratio (R_r) were varied between 0.129 and 0.214, 2.11 and 2.86 for all the drying conditions, respectively. Total colour change (ΔE) varied from 5.30 to 13.19. Vitamin C content decreased, while lycopene content increased with infrared drying. For optimum points, desirability of functions of all targets had satisfactory, very good and excellent desirability values and ranged between 0.54 and 0.99.     

Single-layer drying characteristics and colour kinetics of red chilli

Single‐layer drying experiments were conducted under controlled conditions of temperature, relative humidity (RH) and air velocity to find out the effects of drying conditions and blanching on the drying rate and colour of Thai red chilli. Drying rate increased with an increase of drying air temperature and a decrease of RH. Air temperatures above 65 °C affected the colour of red chilli. Red chilli should be dried at an air velocity equal to or just above 0.50 m s^?1. Above this value, the drying rate becomes independent of air velocity. RH and air velocity have no effect on the colour of red chilli. Faster drying rate and higher colour value was found for the blanched sample rather than the unblanched sample. The Newton and the Page equations were fitted to the experimental data. The Newton equation was found to describe the single‐layer drying of red chilli better than the Page equation.     

Experimental study on drying characteristics of pomegranate peels

Drying kinetics of pomegranate peels has been experimentally investigated in a cabinet dryer. Drying experiments were performed at constant air velocity of 2.0 m/s and initial thickness of 2.8 cm for pomegranate peels, and 3 drying air temperatures of 50, 60, and 70°C. The drying time decreased with increase in drying air temperature. Experimental data were fitted to 10 mathematical models. The fit quality of models on experimental data were evaluated using 3 statistical tests, coefficient of determination, reduced chi-square, and root mean square error. The statistical analysis concluded that the best model in terms of fitting performance was the Midilli et al. model. The effective diffusivity varied from 4.02 to 5.31×10⁻⁹m²/s over temperature range. Temperature dependence of the diffusivity was well documented by Arrhenius-type relationship. The activation energy was found to be 12.72 kJ/mol for pomegranate peels.     

Microwave, air and combined microwave-air-drying parameters of pumpkin slices

Pumpkin slices (Cucurbita maxima) which weighs 50 g with moisture of 9.31 g water/g dry solids, were dried using three drying methods, microwave, air and combined microwave-air. Drying continued until slice moisture reduced to 0.1 g water/g dry solids. Two different microwave output powers 160 and 350 W were used in the microwave drying. Drying treatments in air-drying were 50 and 75 °C and 1 m/s fan speed. The combination drying in which microwave and air-drying were applied together was four different combination levels. Drying periods lasted 125-195, 45-90 and 31-51 min for microwave, air and combined microwave-air-drying, respectively, depending on the drying level. Energy consumption was 0.23-0.34, 0.61-0.78 and 0.29-0.42 kW h, respectively. In this study, measured values were compared with predicted values obtained from Page's semi-empirical equation. Optimum drying period, colour and energy consumption was obtained when microwave and air-drying was applied simultaneously and the optimum combination level was 350 W microwave applications at 50 °C.     

白玉菇中短波红外干燥特性及动力学模型

为提高白玉菇的货架期,采用中短波红外线对白玉菇进行干燥,考察了干燥温度(60、70、80、90℃)和干燥功率(675、900、1125、1350 W)对白玉菇干燥特性的影响,并通过7种常用的农产品干燥模型对干燥过程进行了拟合,建立了白玉菇中短波红外干燥的动力学模型.研究结果表明:干燥温度和干燥功率对白玉菇的干燥过程均有...     

Drying of pomegranate seeds using infrared radiation

Effect of different infrared (IR) power levels on drying kinetics of pomegranate seeds was investigated. The pomegranate seeds were dried at 83, 104, 125, and 146 W IR power levels. It was observed that the power levels affected the drying rate and time. Drying time reduced from 150 to 60 min as the IR power level increased from 83 to 146 W. The experimental data obtained from drying study were fitted with 10 mathematical models to evaluate the drying kinetics of the pomegranate seeds. The Page, Midilli et al., and Weibull models are given better prediction than the other models and satisfactorily described drying kinetics of pomegranate seeds. Effective diffusivity varied from 1.96 to 6.29×10^?11 m²/s and was significantly influenced by IR power.     

Hot air drying of yacon (Smallanthus sonchifolius) and its effect on sugar concentrations

This work aimed to experimentally study the drying behaviour of yacon tubers with and without steam blanching. Drying was carried out for 5 h and 30 min in a forced air dryer at 50 °C, 60 °C and 70 °C. The results indicated that the shortest drying time was obtained at 70 °C for blanched samples, and that the equilibrium water activity values were significantly lower for the blanched samples at all temperatures. The yacon dried without prior blanching showed lowest concentrations of reducing sugars when dried at 70 °C, significantly lower than those dried at 50 °C and 60 °C. This indicates hydrolysis of the fructo-oligosaccharides at 70 °C, a fact verified by the significant increase in reducing sugars content from 36.65 ± 0.54–44.10 ± 0.96% and reduction in the non-reducing sugars from 31.62 ± 0.55–26.18 ± 0.29%.     

INFRARED AND HOT-AIR DRYING OF ONIONS

The combination of infrared (IR) and hot‐air drying of onion slices was explored, and the effects of processing conditions such as drying temperature, slice thickness, air temperature and velocity on onion slice characteristics were studied. The onion slice quality was evaluated on the basis of the color and the pyruvic acid content, an index of flavor. Drying of thin slices of onion (2 mm) at low temperature (60C) with a moderate air velocity (2 m/s) and air temperature (40C) retained greater flavor and color. An empiric equation developed to correlate the drying process variables and the onion slice moisture with the drying time provided a good fit (R² = 0.92). Similar equations developed to correlate the drying process variables and the drying time with the pyruvic acid content provided an excellent fit (R² = 0.96), while the equations fit for the total color change of onion slices were satisfactory (R² = 0.86). Combination drying resulted in shorter drying process time and in better onion slice quality as compared to IR and hot‐air drying applied individually.     

响应面分析法优化热风微波耦合干燥油茶籽工艺

为了优化油茶籽干燥,分别研究了油茶籽的热风和热风微波耦合干燥工艺。热风微波耦合干燥利用Box-Benhnken中心组合实验设计和响应面分析法,以过氧化值(POV)和干燥时间为响应值,优化了不同热风温度、热风速度和微波功率密度时油茶籽的热风微波耦合干燥工艺。经响应面分析得油茶籽的干燥工艺为:在热风温度为58.9℃、热风速度为1.262m/s、微波功率密度为1.972W/g、干燥时间为306min时,油脂的过氧化值为1.0472nmol/kg。热风微波耦合干燥时间比热风干燥节约近3倍,过氧化值减小了7.46%。     

DRYING BEHAVIOR OF CULTURED MUSHROOMS

In this study, the drying behavior of cultured mushrooms with an initial moisture content of 93% (drying basis [ d.b. ]) was investigated experimentally for different slice thicknesses and drying air temperatures, and the suitability of various drying models in defining the drying behavior of mushrooms was determined by statistical analysis. Drying operation was carried out at temperatures of 40, 45, 50 and 60C and at a fixed air velocity of 2 m/s. The slice thicknesses of mushrooms were taken as 2, 4 and 6 mm. The experimental results show that the drying temperature has a significant effect on the moisture removal from mushrooms. However, it is also observed that increasing the temperature above a certain value for large values of slice thickness does not have a considerable effect on the drying rate. It may also be concluded from the experimental results that the increase in the slice thickness slows down the drying rate significantly. Furthermore, the results of statistical analysis show that the most suitable model in defining the drying behavior of mushrooms is the diffusion approach model.

PRACTICAL APPLICATIONS

Mushrooms are soft textured and extremely perishable. They begin to deteriorate shortly after harvest. Because of their short shelf life under normal ambient conditions of temperature and humidity, their preservation has assumed importance. The most common species that is also grown on a large scale in Turkey is the cultivated mushroom, Agaricus bisporus . They are low in calorie and have a delicate, appealing flavor. They contain about 91% water. Drying is the most common preservation method, especially for mushrooms to be used as ingredients for special sauces and soups. Preservation of mushrooms through drying makes it possible to limit microbial growth or other reactions by reducing moisture content, and allows efficiency in transportation and storage.     

Quality improvement of non-sulphited mango slices by drying at high temperatures

An optimum drying routine for producing non-sulphited mango slices has been developed. The interaction of essential drying parameters (air temperature, air velocity, dew point, slice thickness and drying time) on water activity (a_W) and browning was determined. Microbiological stability of the dried product was achieved at a moisture content of 17% wet base (w.b.) corresponding to a_W = 0.6. Browning was monitored by the red colour shade of the product (CIE-Lab chromaticity coordinate a*). Drying air temperature and drying time were shown to be the primary factors influencing product colour and a_W. In contrast to common practice, drying for about 6 h at elevated air temperature (80 °C), instead of 50 or 60 °C for a longer time, was optimal, since significant colour changes of the mango slices were not observed even without the use of any chemical or thermal pre-treatment. Moreover, at increased temperature, drying time was considerably shortened from about 9 h to 6 h, resulting in significant extension of the drying capacity.

Industrial Relevance

The suggested process concept for dried mango slices based on high-temperature drying is of utmost significance for the international marketing of dried fruit products. Chemical pre-treatments such as sulphitation often used to minimise quality deficiencies could be avoided. Sulphitation has been recently under critical consideration with respect to allergen labelling of foodstuffs implemented by EU-Member States in November 2004 (Directive 2003/89/EC) [Directive 2003/89/EC. Official Journal of the European Union, 25.11.2003, pp. L308/15–18 (http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_308/l_30820031125en00150018.pdf)]. Export quality was improved and the drying process simplified, improving the utilisation of drying capacities. Particularly referring to an application of the technology in small- and medium-sized enterprises with limited investment possibilities, the suggested novel drying procedure in mango processing aimed at the optimisation of well-established simple drying methods instead of choosing technically more sophisticated technologies.     

Performance analysis of drying of green olive in a tray dryer

This paper deals with the performance evaluation of a single layer drying process of green olives in a tray dryer using exergy analysis method. Green olive was used as the test material being dried. Drying process was realized at four different drying air temperatures (40, 50, 60 and 70 °C) and a constant relative humidity of 15%. The effects of temperatures and mass flow rates were investigated. Maximum exergy efficiency of the drying chamber was obtained at a temperature of 70 °C and a drying air mass flow rate of 0.015 kg/s with 0.0004 kg/s of olive. The exergy efficiency values were found to be in the range of 68.65%–91.79% from 40 °C to 70 °C with drying air mass flow rates of 0.01 kg/s–0.015 kg/s.     

Determination of microwave drying and rehydration kinetics of green peppers with the bioactive and textural properties

The aim of this study was to determine the effect of microwaves on drying and rehydration kinetics of green pepper varieties (sweet, green, and bell) and the bioactive and textural properties of dried and rehydrated peppers. Drying was performed at 90, 180, and 90 + 180 W and dried peppers were rehydrated at 25, 50, and 70°C. The best drying fits were obtained using the equations of both Sigmoid and Hii et al. for drying, and two term exponential decay was the most appropriate model for rehydration. The lowest and highest final rehydration ratio values were obtained for the peppers dried at 180 and 90 W, respectively at each temperature and pepper variety. Among peppers, bell pepper showed the lowest color change (ΔE) and it was the most potent to recover initial color in rehydration. Peppers had softer texture in both drying and rehydration treatment. Total phenolic content of peppers was reduced around 56–65% compared to the fresh pepper by drying and this decrement was reached up to 87% in rehydrated peppers. Results showed that drying at 180 W and rehydration at 70°C provided faster drying and rehydration as well maintained the quality characteristics of green peppers.